Dear Economist: When should a July-born child start school?

My four-year-old son has a July birthday, which would make him one of the youngest in his class at school. I am thinking of keeping him back a year so that when he does start school, he’ll be bigger and more confident. Is this a good idea?
Sarah Goldberg, by e-mail

Dear Sarah

Other parents think it is. The economists David Deming and Susan Dynarski have found that the percentage of six-year-olds not yet registered at school has quadrupled in the US over the past 40 years, largely because parents are holding back their children.

Being older seems to convey lasting benefits in sports: an unusual number of international footballers are old for their year, for instance. That is surely because the older children are more likely to be selected for the most competitive games with the best coaches. Academic streaming may create a similar effect. An influential piece of research, from Kelly Bedard and Elizabeth Dhuey (also economists), found that the oldest in the class tended to do better not just when five or six but even as college students.

Not every study agrees, and Deming and Dynarski also point out that starting school late has its costs. Still, one thing is certain: since your boy has a mother who is fussing about this sort of stuff, he’s going to do fine no matter what.